Furnace display shows E05, burners do not light, you may hear a click from the gas valve but no flame.

Safety first: If you smell gas, do not operate any switches or use open flames. Evacuate the area and contact your gas supplier or emergency services. Otherwise, turn off power to the furnace before servicing.

• 1. Confirm gas supply: Verify that the manual gas shutoff valve near the Thermia furnace is fully open. Check that other gas appliances (stove, water heater) are working. If none work, contact your gas utility.
• 2. Inspect gas valve wiring: Remove the burner compartment door and locate the gas valve. Check that the wiring harness from the Thermia control board to the gas valve is firmly connected and not damaged or burned.
• 3. Listen for valve operation: Restore power and call for heat. After the igniter glows, listen for a distinct click from the gas valve. If there is no click, the valve may not be receiving power or may be defective.
• 4. Check control board output (advanced): With a multimeter and extreme caution, a technician can measure voltage at the gas valve terminals during ignition. If proper voltage is present but the valve does not open, the gas valve is likely faulty and should be replaced with a Thermia-specified valve.
• 5. Do not attempt gas pressure adjustments: Gas pressure and combustion tuning must be performed by a licensed technician with proper instruments. Incorrect adjustments can cause fire, explosion, or carbon monoxide hazards.
• 6. If E05 persists: Contact a qualified service technician to test inlet gas pressure, manifold pressure, and verify correct operation of the Thermia gas train.